Tumors have a variety of tissue structures, but all tumor tissue components can be divided into two parts: parenchyma and mesenchyme. The mesenchymal component of the tumor is not specific and plays the role of supporting and nourishing the tumor parenchyma. It is generally composed of connective tissue and blood vessels, and the mesenchyme sometimes has lymphatic vessels. Mesenchymal tumors are tumors of the mesenchymal tissue. There are many types of mesenchymal tissue tumors, including tumors of adipose tissue, blood vessels and lymphatic vessels, smooth muscle, rhabdomyosarcoma, fibrous tissue, and bone tissue. Mesenchymal tissue tumors other than bone tumors are also often called soft tissue tumors (soft tissue tumors). Among mesenchymal tissue tumors, benign ones are more common and malignant tumors (sarcomas) are uncommon. There are many neoplastic lesions in the mesenchymal tissues that form clinically visible “masses”, but they are not true tumors.